Low voltage protective gaps provided with arc running surfaces for circulating arcs



Jan. 18, 1966 s. 5M H, JR 3,230,411

Low VOLTAGE PROTECTI GAPS PROVIDED WITH ARC RUNNING SURFACES FOR CIRCULATING ARCS Filed April 1, 1965 2 Sheets-Sheet 1 I [mafia S'aneyfl 5/72/77? (fl;

HEW/5r Jan. 18, 1966 s. R. SMITH, JR 3,230,411 LOW VOLTAGE PROTEC E GAPS PROVIDED WITH 65ARC RUNNING SURFAC FOR CIRCULATING ARCS 2 Sheets-Sheet z Filed April 1, l9

.spacing between electrodes.

United States Patent LOW VOLTAGE PROTECTIVE GAPS PROVIDED WITH ARC RUNNING SURFACES FOR CIRCU- LATING ARCS Sidney R. Smith, Jr., Stockbridge, Mass., assignor to General Electric Company, a corporation of New York Filed Apr. 1, 1963, Ser. No. 269,548 Claims. (Cl. 313231) This invention relates to over-voltage protective devices, and, more particularly to improved low voltage protective gaps provided with are running surfaces for circulating arcs.

As is known to those skilled in the voltage protection art, the main purpose of over-voltage protective devices, such as voltage gaps, is to protect the insulation of the circuits on which the gaps are applied. Such gaps take many forms. They may comprise a pair of rods spaced from each other in axial relationship. These rods or electrodes may be pointed. or they may terminate in spherical surfaces. The gaps may take the form of a pair of opposing horns or are runners, e.g., the well-known horn gap. All such forms, as well as others, have been used to form the gap portions of various types of other protective devices, such as lightning arresters. In any case, the two electrodes forming the gap are spaced at a suitable distance so that the voltage required to spark over between electrodes is less than the withstand voltage of the circuit to be protected.

As the required spark-over level is reduced, it becomes necessary to dimension the gap to have smaller physical In many applications this presents no problem since the current magnitude and duration can be limited by suitable series resistance, as for example non-linear resistance material commonly used in series with the gaps which go to make up lightning arresters. Where the voltage protective level is required to be relatively low, however, the resistance value must be kept lower to avoid a high IR voltage following gap spark over. This, in turn, means that the gap current after spark over tends to be larger and of longer duration, tending to cause damage to the electrode surfaces and degradation of the gap spark-over characteristics. One approach which has been employed to solve this problem, is to make the gaps in the form of horns and to add an auxiliary gapped coil to produce a magnetic field which aids in rapidly moving the are out of the starting point between the horns, or are runners, once spark-over has occurred. However, for low voltage gaps, series gapped coils are undesirable sincethe spark-over voltage of the coil gap adds to the main voltage gap, increasing the over-all voltage characteristics.

It is well known to use voltage gap electrodes provided with divergent horns whereby arcs established in the spark-over portion of the gap tend to move out to the ends of the divergent horns due to the magnetic efiect produced by the current in the electrodes. However, when the distance between the electrodes in the sparkover portion of the gap is 30 mils orless the arc tends to stick or remain immobile in the spark-over portion of the gap. This causes melting or fusing of the electrodes. To obtain the desired low voltage spark-over characteristics a spacing of less than 30 mils is required. The spacing could be enlarged by partially evacuating the spark gap. This would increase the cost of the device. It would also introduce new problems because of the ionization time lag characteristics of partially evacuated gaps.

It has been discovered that an arc gap may be provided with a relatively large space between the main gap electrodes at the spark-over portion of the gap with desirable low voltage characteristics by the use of a trigger Patented Jan. 18, 1966 electrode inserted into the spark-over portion of the main gap electrodes. The trigger electrode is connected electrically to one of the gap electrodes through an electrical impedance and has one portion of the trigger electrode extending into the spark-over portion of the main gap electrodes. The spark-over distance, here termed the trigger gap, between the trigger electrode and either of the gap electrodes is sufficiently small to allow a low voltage to ionize the air between the trigger electrode and one of the gap electrodes. This will cause the trigger gap to spark over, first between the other gap electrode and the trigger electrode and then the one gap electrode and the trigger electrode. Once the arc has been formed between the gap electrodes and the trigger electrode, the arc will be transferred to the main gap electrodes. Since the over-all gap space between the gap electrodes is relatively large, the arc may be readily moved out of the spark-over portion of the gap electrodes and out along the divergent portion of such gap electrodes.

It is, therefore, one object of this invention to provide a novel gap structure which will spark over at low voltages.

Another object of this invention is to provide a novel gap structure having low voltage spark-over characteristics and being provided with sufficient spacing between the electrodes to allow the arc to be readily moved out of the spark-over portion of the gap.

A further object of this invention is to provide a novel gap structure having low voltage characteristics in which the gap electrodes are provided with divergent portions beyond the spark-over portion of the gap and which will readily move the are out of the spark-over portion of the gap to prevent impairment of the low voltage characteristics of the spark gap.

It is a further object of this invention to provide a low voltage gap structure provided with a trigger electrode between the main gap electrodes of the arc gap structure to provide low voltage characteristics and maintain sufficient spacing between the gap electrodes to allow an arc formed in the spark-over portion of the gap to be readily moved out of such spark-over portion.

As is well known, when a gap structure sparks-over it is desirable to prevent the burning of the electrode surfaces before the arc is extinguished. This is accomplished in many gaps by means of moving the arc from the sparkover portion of the gap electrodes to outer divergent portions of the electrodes. As will be understood, when the arc moves out into the outer divergent portions of the gap electrodes the arc is lengthened, thereby increasing the resistance of the arc and thus in effect decreasing the burning characteristics of the arc.

In many applications using voltage gaps the total time duration during which the gap is required to carry current is the duration of one current loop in a 60-cycle circuit, or second. However, in some applications low voltage gaps are required to carry current for a duration of 30 current loops in a 60-cycle circuit, or A second. Obviously with currents of such long duration, a standing arc of even small current will seriously damage the electrodes. Where the current is relatively large, in the order of 1,000 amperes or more, a standing arc will melt and fuse the electrodes in a relatively short time. In a low voltage are. gap it has been found that if large surface arc runners are provided at the extremity of the gap electrodes, the arc may be forced between such large surface are runners, thereby preventing the melting and fusing of the gap electrodes. Damage to the arc runners may also be prevented provided the arc is kept in motion during high current periods. In accordance with this invention, arc runners are provided at the outer extremity of the gap electrodes, the arc runners being designed to cause the are formed between such runners to rotate around the arc runners thereby preventing any substantial burning of the surfaces of the arc runners. Since gaps may be applied in an environment having moisture or corroding fumes, it is desirable that the gap structure be sealed against the atmosphere.

It is, therefore, a further object of this invention to provide a gap structure having a relatively low spark-over voltage level but with unusually high current magnitude and duration withstand ability.

It is also another object of this invention to provide a gap structure in which the foregoing object is achieved without the use of auxiliary coils.

A further object of this invention is to provide a low voltage gap, capable of dissipating currents of unusually high magnitude and duration, in the form of a sealed structure which is thereby capable of resisting the deteriorating effects of environmental atmospheres in which it may be applied.

Another object of this invention is to provide a low voltage gap structure having large surface arc runners designed to cause the arc to circulate about such are runners.

A still further object of this invention is to provide a gap structure in which the divergent portions of the gap electrodes cause the arc to be moved onto adjacent arerunning surfaces to thereby prevent the are from remaining in the divergent portions of the gap electrodes and thus prevent impairing the electrical characteristics of the gap electrodes.

In carrying out this invention in one form a low voltage are gap construction is provided which comprises a pair of gap electrodes having a spark-over portion and diverging outer portions A trigger electrode is placed between the gap electrodes with a portion extending into the spark-over portion of the gap. The trigger electrode is electrically connected to one of the gap electrodes by an electrical impedance. In this manner, a trigger gap is provided between the other gap electrode and the trigger electrode of sufficiently small spacing to allow the sparking over of such trigger gap at desirable low voltage levels. The gap spacing between the main gap electrodes at the spark-over portion is maintained at a sufiiciently large spacing to allow the arc to be moved out of the spark-over portion and along the divergent portions of the gap electrodes. Further, arc runners may be provided adjacent the divergent portions of the gap electrodes, enabling the arc to be forced onto such arc runners. The are runners are designed such that the arc current will cause the arc to rotate about the arc runners, thereby preventing damage to the surfaces of the arc runners.

The invention which is desired to be protected will be particularly pointed out and distinctly claimed in the claims appended hereto. However, it is believed that this invention and the manner in which its various objects and advantages are obtained, as well as other objects and advantages thereof, will be better understood from the following detailed description of a preferred embodiment thereof, especially when considered in the light of the accompanying drawings, in which:

FIGURE 1 is a sectional view taken on the line 1-1 of FIG. 2 showing a preferred form of low voltage are gap structure according to this invention;

FIGURE 2 is a sectional View taken on the line 2-2 of FIG. 1 showing other details of the preferred form of low voltage are gap structure;

FIGURE 3 is a plan view of a preferred form of arc runner made in accordance with this invention;

FIGURE 4 is a perspective view of an additional arc runner which may be used between the arc runners of FIG. 1 to split the are between such are runners into smaller arcs;

FIGURE 5 is a plan view of the arc runner shown in FIG. 4; and

FIGURE 16 is a partial sectional view of an arc gap structure similar to FIG. 1 showing the positioning of additional arc runners, such as those shown in FIGS. 4 and 5.

As earlier noted, in forming a low voltage are gap it is desirable to maintain adequate spacing between the gap electrodes so that an are formed therebetween can be readily moved out of the spark-over portion of the gap to prevent damage to its spark-over characteristics. It has been found that where the spacing of the spark-over portion of the gap electrodes is small, in the order of 30 mils or less, it is very difficult to move the are out of the spark-over portion of the gap. However, to obtain the desired low voltage spark-over characteristics necessary to enable a low voltage to stress the air in the gap to cause an arc to form, it is necessary to have small spacing between the electrodes in the spark-over portion of the gap. Clearly, when the spacing is large enough to allow the arc to be readily moved out of the spark-over portion of the gap electrodes, the potential required to are over the air in such gap is substantially greater than the desired low voltage potential of the arc gap structure. In accordance with this invention both requirements are met by using a trigger electrode between the gap elec trodes with a portion of the trigger electrode extending into the spark-over portion of the gap. The trigger electrode is electrically connected to one of the gap electrodes by means of an electrical impedance to thereby enable the sparking over of the gap first from the electrodes to the trigger electrode and then between the main electrodes.

Reference will now be made to the drawings, in which like numerals are used to indicate like parts throughout the various views thereof. Considering FIGS. 1 and 2 of the drawings, a low voltage are gap structure is shown according to a preferred embodiment of this invention. As shown in FIGS. 1 and 2, the arc gap structure comprises a pair of terminal members 10 and 12 which are placed at opposite ends of the gap structure. The terminal members 10 and 12 are electrically connected to the gap electrodes 14 and 16 to allow an electrical potential to be applied across the spark-over portion 18 of the gap electrodes 14 and 16. As will be understood, the terminal members 10 and 12 will be connected in circuit with the electrical equipment whose insulation is to be protected. The spacing between electrodes 14 and 16 at the sparkover portion 18 is sufficiently large to enable any arc formed in the spark-over portion of the gap to be readily moved out of the spark-over portion 18 and along the divergent portions 20 and22 of the gap electrodes 14 and 16 In order to provide the desired low voltage spark-over characteristics to the spark-over portion 18, a trigger electrode 24 is provided which is mounted between the electrodes 14 and 16. The trigger electrode 24 is insulated from both electrodes 14 and 16 by insulating members 26 and 28, which may be mica plates or any other desired insulating material. The trigger electrode 24 is electrically connected to one of the electrodes, for example electrode 16 in FIG. 1, by means of an electrical impedance indicated as 30 in FIG. 1 and FIG. 2. The tip 32 of the trigger electrode 24 extends into the spark-over portion 18 between the gap electrodes 14 and 16, as shown. Thus, small trigger gaps 34 and 36 are provided between the trigger electrode 24 and the spark-over part of each of the gap electrodes 14 and 16, as shown.

As will be understood, when an electrical potential is placed across the terminals 10 and 12 a voltage stress will be placed across the spark-over portion 18 between the electrodes 14 and 16. However, since the trigger electrode 24 is electrically connected to the electrode 16, the tip 32 of the trigger electrode 24 will be at the same electrical potential as the electrode 16. Since there is no current flowing through the trigger electrode, before areing, there will be no voltage drop across impedance 30.

tion 32, have the same electrical potential as the electrode 16. The entire voltage stress is thus placed initially across the trigger gap 34 between electrode 14 and electrode 24. A small voltage will provide suflicient stress to ionize the air and form an arc in the trigger gap 34 between that electrode 14 and trigger electrode 24.

As soon as the are forms between gap electrode 14 and the tip 32 of the trigger electrode 24, current will flow in the trigger electrode through the impedance 30. This current flow will change the electrical potential between the trigger electrode 24 and the gap electrode 16. Since there is very little resistance in the trigger gap 34 substantially the entire electrical potential across the terminals and 12 will now be formed across the trigger gap 36 between the tip 32 of trigger electrode 24 and the gap electrode 16. Of course, since an arc has already formed between electrode 14 and trigger electrode 24 ionized air is already available in the trigger gap 34, thereby enabling an arc to readily form between the trigger electrode 24 and the lower gap electrode 16.

As will be understood, as soon as the second are forms between the trigger electrode 24 and the gap electrode 16, substantially no current will flow in the impedance 30 inasmuch as there is much less resistance in the trigger gap 36 than in the impedance 30. Therefore, the are will immediately transfer from electrode 14 to electrode 16 since the spark-over portion 18 will have less resistance than two arcs formed across the trigger gaps 34 and 36. This shifting of the arc to a point away from the trigger electrode is also aided by the magnetic field created by the currents in the electrodes 14 and 16. Thus it is seen that by means of the trigger electrode 24 the spark-over portion 18 of electrodes 14 and 16 will be caused to are over at low voltage potentials thereby forming the desired low voltage are gap.

When the are forms in the spark-over portion 18, the current flow through the electrodes 14 and 16 causes a magnetic force which forces the arc to move out along the divergent portions 20 and 22 of the gap electrodes 14 and 16. As will be understood, as the arc is formed in the spark-over portion 18 a magnetic flux is also generated by the current flow within the arc. The flux, which is generated in the spark-over portion 18 on the side adjacent the trigger gap 24, is narrowly confined within a small space, as can be seen from an inspection of FIG. 1. However, the flux which is generated on the opposite side of the arc within the divergent portions 20 and 22 of the electrodes 14 and 16 is provided with a substantial expansion area. Therefore, as will be understood, the force of the magnetic flux on the arc, which is at right angles to the flux field, will be greater on the side of the are adjacent the trigger gap 24 and will force the arc out along the divergent portions 20 and 22 of the gap electrodes 14 and 16. In this manner it will be seen that once the arc is formed in the spark-over portion 18, the arc is caused to move out on the divergent portions 20 and 22 of the electrodes, thereby preventing the are from sticking in the spark-over portion and preventing any deterioration of the low voltage level of the arc gap structure.

As will be apparent from FIG. 2 of the drawings, the divergent portions 20 and 22 of the gap electrodes 14 and 16 are narrow members as compared to the overall width of the electrode members 14 and 16. The sparking point 32 of electrode 24 fits into the spark-over portion 18 of the electrodes. Thus it will be apparent that the arc will form within the spark-over portion 18 between the narrow portions of the electrodes. The narrow portion of the electrodes concentrates the current providing the magnetic force to cause the arc to run out of the spark-over portion 18 and along the divergent portions 20 and 22 of the electrodes. In this manner there is provided a low voltage arc gap which will spark over at very low potential while at the same time providing ease of movement of the are which forms within the spark-over portion of the electrodes to prevent damaging of such electrodes.

As one example of the preferred embodiment of this invention, the trigger electrode 24 has been connected to a main gap electrode, such as 16, by means of a 50,000 ohm resistor. In another case a capacitor was placed in parallel with the resistor, the capacitor being approximately .001 microfarad. The spacing between the main electrodes, such as 14 and 16, was in excess of 30 mils. In each instance it was found that an arc was formed in the gap with potentials of 2500 volts. The are formed readily moved out of the gap and onto the divergent portions 20 and 22 of the electrodes.

Of course, as will be readily understood, many times it will be necessary for the low voltage gap structure to be used in an environment which involves either moisture or corroding films. Obviously, in such environments it is desirable that the structure be sealed against the atmosphere. In order to provide the desired sealing of the low voltage gap structure, shown in FIGS. 1 and 2, a casing member 40 is provided substantially surrounding the low voltage gap structure, as is clearly shown in FIGS. 1 and 2. In FIG. 2 the casing member is shown as an annular member. As will be understood the casing member 40 may be any shape desired; however, the preferred embodiment is annular for reasons which will hereinafter appear. The upper and lower portions of casing 40 are sealed by insulating members 42 and 44, which may be for example, a water resistant plastic such as phenolic, and have outer circumferential portions which fit under the spun over ends 46 and 48 of the casing member 40, as is shown most clearly in FIG. 1 of the drawings. If desired, a flexible insulating material, indicated at 50, may be utilized between the spun over members 46 and 48 of the case 40 and the insulating end members 42 and 44 to ensure a substantially tight seal for the end members. An opening is provided through the end members 42 and 44 for the terminals 10 and 12, as is shown most clearly in FIG. 1. Beneath the end members 42 and 44 a gasket may be provided, indicated at 52 and 54 of the drawing, between the end members 42 and 44 and the arc runners 56 and 58, which runners will be described more fully hereafter. The gasket members 52 and 54 are preferably of a flexible insulating material such that when the ends 46 and 48 of casing 40 are spun over the end members 42 and 44 the gasket material 52 and 54 will be compressed to form a tight seal about the arc runner 56 and 58 to prevent entry of any moisture or corroding fumes into the arc gap structure.

The arc runners 56 and 58 are provided between terminals 10 and 12 and the gap electrodes 14 and 16, as shown in FIG. 1. The are runners 56 and 58 are preferably annular members conforming substantially to the shape of the casing 40, as will clearly appear from an examination of FIG. 2. The are runners are dished, as

is shown at 60 and 62 in FIG. 1, so that the outer extremities of the arc runners, in the preferred embodiment, the outer circumferential portions, will be in substantially the same plane as the extremities of the diverging ends 20 and 22 of the gap electrodes 14 and 16. By means of dishing of the arc runners 56 and 58, in the manner shown in FIG. 1 of the drawing, when the arc is at the extremities of the diverging portions 20 and 22 of electrodes 14 and 16 it may be readily forced out on to the outer circumferential portions of the arc runners 56 and 58 by means of the magnetic flux which is built up about the are extending between the gap electrodes, in the manner hereinbefore described. After the arc has been forced on to the outer circumferential portions of the arc runners 56 and 58 it is desirable, as hereinbefore discussed, to cause the arc to circulate about the are runners to prevent any burning or pitting of the surfaces of the arc runners. In order to accomplish the circulation of the arc, the arc runners are formed with spirallyshaped cuts, in the manner shown in both FIGS. 2 and 3 of the drawing.

Referring now to FIG. 3 of the drawing, there is shown a top plan view of one of the arc runners, for example are runner 56. As can be seen, are runner 56 is provided with two openings 64 and 66 in the central portion thereof and extending from the openings 64 and 66 are the spiral cuts 68 and 70. As will be apparent from FIG. 3 of the drawing, the spiral cuts 68 and 70 extend from the openings 64 and- 66 in the manner of a spiral across the dish-shape portion 60 of the arc runner to the circumferential extremity of such arc runner. Only two spirally-shaped cuts are shown in FIGS. 2 and 3 of the drawing, and in the preferred embodiment it has been found that two spiral-shaped cuts are sufficient to provide the desired rotation of the are between the arc runners.

However, it will be understood that a larger number of spiral cuts may be provided, if desired.

There is shown in phantom lines in FIG. 3 the terminal and one of the diverging ends of the gap electrode 14 to more clearly indicate the operation of the are runners. As will be apparent, when the arc is forced from the ends 20 and 22 of the electrodes 14 and 16 on to the arc runners 56 and 58 a current will be caused to flow from one of the terminals, for example terminal 10, through the arc runner 56, the are between the arc runners, the arc runner 58 and the terminal 12. From an inspection of FIG. 3 it will be apparent that the current flowing from the terminal 10 will flow substantially in the dot-dash path, 72 indicated on FIG. 3, to the root of the are, indicated by the dot-dash circle 74, on are runner 56. The current will flow from terminal 10 about the dot-dash line 72 between the spiral cuts 68 and 70 and to the root of the arm 74. Current there flows through the arc to the lower arc runner 58 and back between the spiral cuts in the lower arc runner 58 to the lower terminal 12. This current flow will create a magnetic flux field which will tend to force the are formed at are root 74 in a clockwise direction about the arc runner 56, as viewed in FIG. 3. Of course, it will be obvious that were FIG. 3 reversed; that is, turned over, then the arc would be forced to rotate in a counter clockwise direction. Thus it will be seen that by means of the spiral cuts 68 and 70 in the arc runner 56 and similar cuts 76 and 78 in the arc runner 58, as shown in FIG. 2, the are formed between the arc runners may be caused to rotate about the outer circumferential portion of the arc runners. It has been found that arcs having a current in excess of 1,000 amperes may be rotated in this manner, without damage to the are running surfaces 56 and 58.

Of course, it will be obvious to those skilled in this art that the arc runners 56 and 58 may also find utility in arc gaps of relatively high potential. For example, in any arc gap using diverging ends or horns, such as diverging ends 20 and 22, it may be desirable to move an are from such ends to are runners. In such instances, the arc gap could be one without a third electrode. Clearly, once an arc is formed in the gap, whether from high or low potential, the arc runners 56 and 58 will be useful to rotate such are in the manner hereinbefore described.

Referring now to FIG. 2 of the drawing there is shown a pair of annular insulating members 80 and 82 which form a channel about the outer circumferential portion of the arc runners 58 and 56. It will be apparent that the arc circulating about the outer circumferential portion of the arc runners will be confined to the channel between insulating members 80 and 82. As can be seen in FIG. 2, insulating member 82 is provided with a slotted portion 84 through which the divergent portions 20 and 22 of the electrodes 14 and 16 extend, enabling the arc to be moved from the gap electrodes on to the arc runners, in the manner hereinbefore described. From the above it will be obvious that after the spark-over portion 18 of the gap electrodes 14 and 16 has formed an arc therein the arc is moved out along the diverging end portions 20 and 22 of the gap electrodes 14 and 16 and then on to the outer circumferential portions of the arc runners 56 and 58. The arc runners 56 and 58 cause the arc to circulate about the arc runners in the channel formed by the insulating members and 82, constantly moving the are about the surface of the arc runners to prevent pitting of the are running surfaces.

In some instances it will be apparent that it will be desirable to split the are formed between arc runners 56 and 58 into smaller arcs for purposes of quenching or extinguishing the arc and restoring the dielectric of the arc gap structure. In order to provide for splitting of the are between the arc runners 56 and 58, the ring member shown in FIG. 4 may be utilized. As is shown in FIG. 4, a ring member 86 is provided which is in the form of a metallic member, such as for example copper, which is folded upon itself, as indicated at 88. The folded metal is formed into an annular member or ring member as is shown in FIG. 4. As will be understood, by folding the member on itself, current will flow in the member from the top to the bottom portions through the metal member. That is, current will be caused to flow from the top portion around the fold 88 and into the bottom portion. It has been found that even if the ring member is flattened tightly upon itself that the normal oxide which forms on the surface will provide sufficient insulation to cause the current to flow around the folded portion of the ring member. However, if desired, a layer of insulating material may be applied between the adjacent surfaces of ring member 86. In FIG. 4, the ring member is shown with exaggerated spacing for a clearer understanding of its formation.

The ring member 86 is provided with a plurality of inwardly extending notches, as indicated at 90, on both the upper and lower portions thereof, as shown in FIG. 4. The shape of the notches is more clearly shown in FIG. 5 of the drawing which is a plan view of the ring member shown in FIG. 4. As can be seen, the notches 90 extend angularly from the inner diameter of ring member 86 into approximately the center of the ring member between the inner and outer diameter thereof. The notches 90 are wider at the opening at the inner diameter than at the apex of the notches, as is clearly shown in FIG. 5. As will be understood, when the arc is rotating between the arc runners 56 and 58 the arc will tend to form a U-shaped are about the inner diameter of the ring member 86. However, as the arc approaches one of the notches 90 in its rotation about the arc runners 56 and 58, the arc will tend to straighten between the arc runners and travel into the notch formed in the ring member 86. When the arc member reaches the apex of one of the slots 90 the resistance to the are moving again to the inner diameter of the ring member 86 will be greater than the resistance required to cause the arc to split about the ring member. Therefore, the arc will continue its rotation, having formed a plurality of smaller arcs between the arc runners 56 and 58 and a ring member 86 inserted between the arc runners 56 and 58. As will be understood, the current flow in the ring member 86 will aid in rotating the arc.

The preferred construction utilizing the ring member 86 for splitting the are between arc runners 56 and'58 is more clearly shown in FIG. 6 of the drawing. As can be seen from FIG. 6, a pair of arc splitting ring members 86 and 92 are provided between arc runners 56 and 58.

Ring member 92 will be the same type as previously described for ring member 86. The members are shown as being embedded in the insulating member 80 to hold such members in a desired equidistant position between each other and the arc runners 56 and 58. As will be apparent, as the arc rotates between members 56 and 58 it will enter one of the plurality of channels or slot members 90 in the ring members 86 and 92 and will then be split into three separate arcs, one are formed between the arc runners 56 and arc ring member 86, a second arc formed between the ring member 86 and the ring member 92 and a third arc formed between the ring member 92 and the are runner 58. In this manner the arc may be split into smaller arcs, thus more readily enabling the quenching of such arcs, for example when the potential passes through current zero, thereby restoring the dielectric value of the arc gap structure.

From the above it will be apparent that there has been provided an arc gap structure which may be utilized for arcing on low voltages, and which may be readily able to sustain arcs having a large current and being of substantially long duration. Thus it is seen that the invention hereinbefore described has all the objects and advantages hereinbefore set forth. While there has been shown and described the present preferred embodiment of the novel low voltage are gap structure of this invention, it will be apparent to those skilled in the art that various changes may be made, such as for example in the particular shape of the device, or in the particular shape of the various electrodes, all without departing from the spirit and scope of the invention as defined in the claims appended hereto.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An arc gap structure comprising a pair of metallic terminals connectable across an electrical potential, a pair of arc runners mounted between said terminals, each of said arc runners being electrically connected to one of said terminals, a pair of gap electrodes mounted between said are runners, each gap electrode being electrically connected to one of said arc runners, a pair of electrical insulation members mounted between said gap electrodes and electrically insulating said gap electrodes from each other, and a trigger electrode mounted between said insulation members and electrically connected to one of said gap electrodes through an electrical impedance, said gap electrodes being shaped to provide a narrow spark-over portion with outer portions diverging from said spark-over portion, said trigger electrode having a portion thereof within said narrow spark-over portion of said gap electrodes and said are runners being pro vided with spiral cuts therein extending from the terminal connected portions thereof to the outer ends.

2. An arc gap structure as claimed in claim 1 in which additional arc runners are provided between said pair of arc runners.

3. An arc gap structure as claimed in claim 2 in which said additional arc runners comprise a pair of transversely spaced substantially parallel metallic wall members connected at one end.

4. An arc gap structure as claimed in claim 3 in which said additional arc runners are provided with a plurality of angular notches spaced about said additional arc runners.

5. An arc gap structure comprising in combination a casing member having insulated end members, said casing being sealed from the outer atmosphere, a pair of terminal members mounted on the opposite ends of said casing, 21 pair of spiral arc runners mounted within said casing with each of said pair of arc runners being electrically connected to one of said terminals, a pair of gap electrodes mounted within said casing forming a spark gap, each gap electrode being electrically connected to one of said are runners, a pair of insulating members mounted within said casing between said pair of gap electrodes and a trigger electrode mounted between said insulating menabers and having a portion thereof extending beyond said insulating members and between said gap electrodes, sai d trigger electrode being electrically connected through an electrical impedance to one of said gap electrodes, said gap electrodes being shaped to provide a spark-over portion and diverging outer portions, the spark gap structure operating to short circuit excess potential by means of sparking said spark gap, first forming an are between the other of said gap electrodes and said trigger electrode and then said oneof'said' gap electrodes and said trigger electrode, thereby sparking over-said spark-over portion, the arc in said spark-over portion moving out to said diverging outer portions of said gap electrodes through the magnetic field generated by the current flow within said gap electrodes and said arc, said are then moving to said spiral runners through the force of said magnetic field and then rotating about said spiral runners through the force of the magnetic field generated by the current flow within said spiral runners.

6. An arc gap structure as claimed'in claim 5 in which additional arc runners are provided mounted between said pair of spiral arc runners.

7. An arc gap structure as claimed in claim 5 in which additionalarc runners mounted between said pair of'spiral arc runners, each of said additional arc runners comprise a pair of transversely spaced substantially parallelmetallic wall members connected at one end, each said additional arc runner having a plurality of spaced angular notches, whereby said are rotating between said spiral arc runners will be split into smaller arcs rotating be tween said additional arc runners, and between said spiral are runners and said additional arc runners.

8. An arc gap structure comprising, in combination, a pair of spaced electrodes forming an arc gap, said spaced electrodes having diverging end portions, a pair of spiral arc runners electrically connected to said electrodes, said spiral arc runners having annular are running extremities, a portion of said are running extremities being adjacent to and coplanar with said diverging end portions of said electrodes.

9. An arc gap structure comprising, in combination, a pair of terminal members, a pair of arc runners between said terminals and electrically connected thereto, a pair of electrodes between said are runners and electrically connected thereto, said electrodes forming an arc gap and having diverging end portions, said are runners having annular extremities with portions thereof extending beyond said diverging end portions of said electrodes, said are runners having spiral cuts therein extending from the terminal connected portions thereof to said annular extremities.

10. A voltage gap structure comprising a pair of gap electrodes having a spark-over portion and divergent end portions, a pair of insulating members between said gap electrodes, a trigger electrode mounted between said insulating members and having a portion extending into said spark-over portion, said trigger electrode being electrically connected to one of said gap electrodes through an electrical impedance, and a pair of arc runners mounted on opposite ends of said gap structure, each of said are runners being electrically connected to one of said electrodes, said are runners extending beyond said divergent portions of said electrodes and being provided with spiral cuts therein.

11. A low voltage gap structure for short circuiting low voltage electrical potentials comprising a pair of electrodes, said electrodes being shaped with a spark-over portion and a pair of divergent end portions, a pair of insulating members separating said gap electrodes and a trigger electrode mounted between and in direct contact with said insulating members and having a portion thereof extending into said spark-over portion, said trigger electrode being electrically connected through an electrical impedance to one of said gap electrodes whereby when said gap structure is subjected to an electrical potential above its spark-over value an arc will form between the other of said electrodes and said trigger electrode and then between said trigger electrode and said one electrode.

12. A low voltage gap structure comprising, in combination, a pair of divergent electrodes, a central trigger electrode positioned between said pair of electrodes and electrically connected to one of said pair of electrodes through an impedance and a pair of spiral arc runners adjacent to said pair of divergent electrodes.

13. A low voltage gap structure comprising, in combination, a pair of divergent electrodes, a central trigger electrode positioned between said pair of electrodes and electrically connected to one of said pair of electrodes through an impedance, and a cooperating pair of are runners surrounding said pair of electrodes, said pair of arc runners having a plurality of spiral-shaped cuts.

14. A low voltage gap structure as claimed in claim 13 provided with a sealed casing enclosing said electrodes and said arc runners and a pair of terminals electrically connected to said pair of electrodes extending from said casing.

15. A spark gap device having a pair of axially spaced and aligned parallel metallic disc are runners provided respectively with central terminal members, said runners having narrow gaps extending spirally outward in the same direction from their central terminal members to their periphery for producing an electromagnetic force having both a radial and a tangential component on an arc between said runners for urging said arc to move circumferentially along the periphery of said runners, and means for dividing said are into two series arcs comprising a pair of flat parallel split metallic rings positioned in the gap between the peripheries of said are runners with their fiat surfaces parallel the surfaces of said are runners, said rings having a series of circumferentially spaced axially registering slots extending angularly out ward from their inner side in the direction of circumferential movement of said arc for trapping said arc therein, said rings being electrically connected together at but one pair of adjacent ends so as to leave them split, the connected ends being such that are current flowing in said rings through said end connection will form a loop trailing the circumferential motion of said are for reinforcing the tangential electromagnetic force on said are and forcing said arcout of a slot in which it is trapped and onto the flat surfaces of said rings.

References Cited by the Examiner UNITED STATES PATENTS 2,089,555 8/1937 Hull et al 3l5-60 X 2,565,945 8/1951 Bockman et al. 313-325 X 2,906,922 9/1959 Huber 315-59 FOREIGN PATENTS 114,056 10/ 1900 Germany.

JOHN W. HUCKERT, Primary Examiner.

DAVID J. GALVIN, D. E. PITCHENIK,

Assistant Examiners. 

5. AN ARC GAP STRUCTURE COMPRISING IN COMBINATION A CASING MEMBER HAVING INSULATED END MEMBERS, SAID CASING BEING SEALED FROM THE OUTER ATMOSPHERE, A PAIR OF TERMINAL MEMBERS MOUNTED ON THE OPPOSITE ENDS OF SAID CASING A PAIR OF SPIRAL ARC RUNNERS MOUNTED WITHIN SAID CASING WITH EACH OF SAID PAIR OF ACR RUNNERS BEING ELECTRICALLY CONNECTED TO ONE OF SAID TERMINALS, A PAIR OF GAP ELECTRODES MOUNTED WITHIN SAID CASING FORMING A SPARK GAP, EACH GAP ELECTRODE BEING ELECTRICALLY CONNECTED TO ONE OF SAID ARC RUNNERS, A PAIR OF INSULATING MEMBERS MOUNTED WITHIN SAID CASING BETWEEN SAID PAIR OF GAP ELECTRODES AND A TRIGGER ELECTRODE MOUNTED BETWEEN SAID INSULATING MEMBERS AND HAVING A PORTION THEREOF EXTENDING BEYOND SAID INSULATING MEMBERS AND BETWEEN SAID GAP ELECTRODES, SAID TRIGGER ELECTRODE BEING ELECTRICALLY CONNECTED THROUGH AN ELECTRICAL IMPEDANCE TO ONE OF SAID GAP ELECTRODES, SAID GAP ELECTRODES BEING SHAPED TO PROVIDE A SPARK-OVER POR- 